Eczema herpeticum is a rare, painful skin rash usually caused by the herpes simplex virus (HSV). HSV-1 is the virus that causes cold sores, and it can be transmitted through skin-to-skin contact.

The condition was initially called Kaposi varicelliform eruption, after the person who first described it and thought the eruption looked like chickenpox.

EH most commonly affects infants and young children who have eczema or other inflammatory skin conditions. But it can also affect adults.

EH is treated with antiviral drugs, and it can become severe and life-threatening if not treated quickly. The viral infection is contagious. If you have EH, be careful not to spread it to other people who have eczema or compromised immune systems.

Although EH is uncommon, its occurrence has reportedly been increasing in recent years. Keep reading to learn how to identify it, what causes it, and more.

The EH rash usually affects the face and neck area, but it can be seen on any area of the body, including skin that’s unaffected by eczema.

EH typically starts suddenly with clusters of small, fluid-filled blisters that are painful and itchy. The blisters all look alike and can be red, purplish, or black. The rash can spread to new sites 7 to 10 days after the first outbreak.

The blisters ooze pus when they break open, and then the lesions crust over. The EH rash heals in two to six weeks. It can leave scars.

EH is most often caused by HSV-1. It can also be caused by the genital herpes virus HVS-2, or some other viruses. EH usually erupts 5 to 12 days after contact with a person who has HSV.

Some people with eczema can have ordinary cold sores that don’t spread. It isn’t known exactly why others with eczema develop a more widespread EH infection, but the reason likely involves the person’s immune system and severity of their atopic dermatitis.

Children with eczema are the most common group to have EH. But only a small percentage of children and others with eczema develop EH. People with severe or untreated eczema are more likely to be affected.

Eczema damages the outer layer of your skin, leaving it dry, sensitive, and more vulnerable to infection. Other suggested risk factors are the lack of antiviral proteins and a lack of cells that promote antivirus immune responses.

A 2003 study found that people with EH had significantly earlier onset of eczema and significantly higher levels of the antibodies produced by their immune system to combat allergies.

People who have damaged skin resulting from other skin diseases or burns are also at risk.

Some prescription skin creams, such as tacrolimus (Prograf), that affect the skin’s immune system may also increase your risk.

Your doctor can likely diagnose EH by its appearance, but they may want to confirm the diagnosis. This is because EH can resemble some bacterial infections, like impetigo. It also can look like a severe flare-up of eczema or other skin issues.

Your doctor will probably have you take systemic antiviral drugs immediately if they think you have EH. Because EH can have serious complications, your doctor likely won’t wait for tests to confirm the presence of the virus.

An EH diagnosis can be confirmed by taking a smear of a blister to check for the virus. Several tests are available to identify the virus, including culturing the sample, identifying antibodies to the virus, or examining it under a light microscope.

It’s also possible to have a secondary bacterial infection, which should be identified for proper treatment.

If left untreated — or not treated soon enough — EH can lead to blindness (though this is rare) and other complications. If the lesions are near your eyes, your doctor should refer you to a specialist for evaluation. HSV can infect your eyes, damaging the cornea.

A 2012 study recommends that doctors routinely check eczema outpatients for signs of EH, because of its potential seriousness. It’s usually considered an emergency, and quick diagnosis and treatment are essential.

Your doctor will prescribe an antiviral drug, such as acyclovir (Zovirax) or valacyclovir (Valtrex), to be taken for 10 to 14 days until the EH lesions heal. If you’re too ill to take drugs by mouth, your doctor may prescribe intravenous antivirals.

Some severe cases may require hospitalization.

If you also have a bacterial infection with EH, your doctor will prescribe antibiotics.

Antiviral drugs will stop the EH outbreak, but the symptoms can come back again. Its return is usually milder after the first attack.

Getting treatment as soon as possible for EH can reduce your risk of complications. Antiviral drugs typically clear up your EH in 10 to 14 days. EH can recur, but recurrences aren’t as common. When it does come back, it’s usually milder.

If you have eczema, you can prevent EH by avoiding contact with someone who has a cold sore. You should also avoid using anything that has touched the mouth of someone with a cold sore, such as a glass, fork, or lipstick.